Several techniques of "solder leveling" have been developed for obtaining uniformly thick coatings of solder on the order of 0.0003 to 0.0006 inches to parts such as printed circuit boards. According to one technique, after the board has been coated with solder by, for example, immersion in a liquid bath of solder, it is rotated so as to throw off the excess solder from the board by centrifugal forces. Apparatus for so leveling the solder is commonly known as a "Gerry Solder Slinger." This technique has not worked out satisfactorily and is not in general use. A second technique is to use hot oil jets and project these jets onto the surfaces of a part which has been immersed in molten solder to remove the excess solder in a controlled fashion. This technique has not been entirely satisfactory because it is difficult to obtain uniform thickness and it is hazardous because of the fact that the hot oil must be at a temperature near the flash point of the oil. Also, the technique is also somewhat messy. A third technique is leveling by means of hot air and, in this technique, the part is immersed in molten solder and, while it is being removed, is subjected to air jets which blow off the excess solder. This technique has gained some success and apparatus for carrying it out is manufactured by Gyrex, Electrovert and Hollis.
The principal objects of this invention are to provide a simplified method and apparatus for solder leveling which avoids the disadvantages of the prior art by separating the means for heating the solder from the means for effecting its removal so that optimum performance of each may be provided independently of the other and, hence, a more efficient use of energy less complexity of equipment and control and, hence, a substantial saving in the cost of equipment.